Machining processes, such as milling, turning, broaching, shaping, and hobbing, are processes that require relative motion between the work and the tool. In conventional linear processes (shaping and broaching) the cutting speed, i.e., the velocity of relative motion between work and tool is equal to the feed velocity. In conventional rotating processes (turning, hobbing, and milling) the rotation of the work or tool allows cutting speeds that are greater than the feed velocity by typically two orders of magnitude or more.
Traditionally, each of the cutting processes has been performed by a machine designed and built specifically for that process. For example, a typical turning machine, or lathe, rotates the workpiece at high velocity against a tool moving on a linear path at a low velocity. A conventional mill rotates a tool at high velocity against a workpiece moving on a linear path at low velocity.
More recently, computer numerically controlled mill/turn machines have become available. Milling on these machines has been accomplished by substituting rotation of the work at very low velocities for linear feed at low velocity. The rotational speed of the work emulates the feed velocity of conventional milling, typically one to ten feet per minute. The rotational velocity of a milling tool typically falls between 100 and 10,000 feet per minute, with most operations performed between 500 and 2,000 feet per minute.